That personality drove her to the top of a sport that allowed no Olympic aspirations when she took it up over a decade ago. And that drive has secured her place in the sport's history no matter what happens in her semifinal bout Wednesday against China's world champion, Ren Cancan.

Esparza and middleweight teammate Claressa Shields are among the 12 medalists in a tournament receiving widespread praise and driving international interest in an amateur sport that's decades removed from its most dynamic days. The women have upstaged the men as the best thing in the London ring, and not just for the novelty.

The quarterfinal rivalry bout matching Ireland's Katie Taylor and Britain's Natasha Jonas had the most electric atmosphere of the tournament, yet the quality of boxing also was undeniably top-notch. No less an authority than Amir Khan, the British silver medalist in Athens and now a successful pro, said he thinks Taylor could beat many of the men in her weight category in London.

"When you see women's boxing at the highest level, how can you argue that women aren't just as good as the men?" Jonas asked.

The field of medalists fighting Wednesday reflects that talent.

Russia, China and the U.S. team will take home two medals apiece. The other winners range from the expected - Taylor, the pound-for-pound champion of the women's game - to the delightfully unexpected: lightweight Mavzuna Chorieva, who clinched Tajikistan's first-ever Olympic boxing medal with an upset win over China's Dong Cheng.

Esparza fit in comfortably with the world's best in recent weeks, and her talent has made her a bigger name than even she realized. Esparza has done commercials for Cover Girl makeup and Coca-Cola in recent months, and Kobe Bryant, LeBron James and Carmelo Anthony asked her to pose for a photo with them in the Olympic Village while she was hitting the pads with her coach.

Thanks to a first-round bye in this relatively small tournament, Esparza had to win just one Olympic bout to secure a medal - although the women have fought for years just to reach this stage.

"It took like 50 fights to get here, so I don't really see it that way," Esparza said. "I see that I got a definite blessing in the brackets, and I think it was well-deserved, because my brackets (in other tournaments) have been horrible. ... I deserved that bye, and it took me a long time to get here."

Esparza and Shields both have fathers who love the intensity and violence of boxing - just not necessarily for their daughters.

Esparza's father, David, hoped his two sons would become boxers, but Marlen showed a talent they couldn't match. David initially was reluctant, but saw his daughter's passion for the sport and embraced it.

Clarence "Cannonball" Shields always wanted a son who could share his love of boxing, particularly after his own amateur career. He spent seven years of Claressa's youth in prison, but piqued her interest in boxing with stories of Laila Ali and his favorite fighters. Claressa pestered him for two years to try boxing until he relented when she was 11.

"I have a strong determination not to lose," Shields said. "I feel like growing up, I lost so much. I just want to be a winner. I love boxing, I put all my time into boxing, and I feel like I deserve to win."

While Esparza is a chiseled, poised technician in the ring, Shields fights on ample reserves of emotion and power. Shields paid close attention to U.S. coach Gloria Peek's instructions between rounds of her victory over Sweden's Anna Laurell, yet she also kept her ears open to instructions shouted from the stands by a coach who knows her even better.

Jason Crutchfield has been training Shields for years at Berston Field House in Flint, Mich., and thinks of Shields as his daughter. His instruction from the stands is mostly to direct her mind, reminding her of a game plan that sometimes doesn't seem like fun when her fearsome fists are flying.

"I'm boxing in there. I just happen to hit hard," Shields said. "That's how I was taught. I wasn't taught to load up. If I was to load up on every punch, I would have been stupid tired in that last round, and she would have won. I was just being sharp, and I just happen to hit hard. I've been paying attention to the point system, I really have."

Shields' path to a gold medal got clearer with the shocking loss of top-seeded Savannah Marshall of Britain, who beat Shields at the world championships - although Shields wasn't happy.